You would need a serious converter as you're going from digital to analog. You can get cards that do component output, but I haven't been very impressed with the ones I've tried (Nvidia 7200GS & 8500GT).
If your card has a DVI-I output (i.e. DVI connector, but can put out VGA or DVI), then you should be able to find a VGA to component converter - probably looking at $150+ for a good one though.
Some older set-top boxes had DVI connectors on them that could output analog component - for those you just need an adapter cable.
BTW, what are the questionable results? Sync/picture drop-out problems, or poor colour, etc? If it's the latter, 8x00 series Nvidia cards can be set to output a different colour scheme over HDMI (YCrCb444 instead of RGB) - it usually fixes any picture quality disappointment. With these cards, you can have DVI at the PC end & HDMI at the TV end (or HDMI @ both ends) to access the setting, but DVI to DVI doesn't allow it (I think).
Justin